The goals of this resubmission of a R29 application are to determine the molecular mechanism of salivary amylase binding to oral streptococci, and to assess the role of this interaction in the context of oral microbial ecology. Studies described herein will characterize and identify the gene coding for the amylase-binding component(s) from Streptococcus gordonii. Additional studies will assess the extent of amylase-bacterium interactions in vivo by determining the proportion and spectrum of amylase-binding bacteria on various oral surfaces, by examining genetic relationships between amylase-binding bacteria, and by determining the in vivo location of amylase in dental plaque by immunogold-electron microscopy. Further experiments will assess the role of amylase in dental plaque formation using two in vitro model systems; the saliva-coated hydroxyapatite model, which mimics the initial adhesion of bacteria to teeth, and a coaggregation model, which mimics plaque maturation. Amylase-binding deficient mutants, amylase-binding components, antibody reagents and fresh dental plaque isolates obtained through the course of the proposed experiments will be used in these model systems. These studies may provide a more complete understanding of the interaction of amylase with oral bacteria, which may serve as a useful paradigm for future studies of other salivary-bacterial interactions. Ultimately, this knowledge may suggest methods to prevent dental plaque formation.